Had several requests to measure the focusing speed of the 6D vs 5Diii vs 5Dii using a Speedlite (in this case 600ex) in low light conditions. Its a redo of the other focusing test I did this week, only this time using the red-af assist light.

I should note 2 things: the 6D does very well even without the AF assist beam. The 6D & 5Diii both feel as if there are 2 stages of focus, a larger followed by a smaller step. The 5Dii seems to lack this.

Very interesting results. Do you have another model of flash that you can repeat the test with to help determine if it is the body or flash or specific combination? I'm still with out my T1i and can't do the same test yet, but will soon I hope. Thanks again!

I have heard that the 5D3 (and I assume the 6D as well) does a focus confirmation in acquiring focus. That is, it achieves focus, then does a confirmation check before shutter release. You can overide this in the menu by changing the shutter release priority from focus priority to shutter release priority in the AF menu. This double confirmation of focus acquisition is new with the 5D3, not a function of the 5D2 AF. This may be the 2nd stage of AF that Michael is noticing, and probably part of the reason this camera seems to have a higher 'hit' ratio with regards to in focus images that most users, including myself, seem to get with this camera as compared to older Canon cameras.

Zlatko

I don't have a 1D series camera currently, but in the past I always had the feeling that the 1D series had a bit of extra lag when using flash compared to any of the xxD series. I believe this wasn't the case with the original 1D, but started with the 1DII or 1DIIN. It may be that the 5D3 has inherited this from the 1D series, along with the AF system generally, perhaps trading speed for accuracy.

How did you determine that focus was achieved? I place the camera in 1 shot AF so that it will not fire until focus is achieved, and do a full button press. The camera fires as soon as focus is achieved, which can be long before the AF indicator lights. So, are you measuring time for focus to be reached, or time for the AF indicator to light?

Someone stated this is not working. Images are OOF. It may be on Canon forums. I have to say. I keep testing this and it and I think it is working.

Only time it takes an extra second is when I really put the lens OOF on purpose. It takes second the the USM to bring it home. Even them my shot was in prefect focus.

I'm going to continue testing this. I have not gone live with this yet. More tests from other people would be helpful.

I just thought of something while writing this. I had also read that the first time on a new subject the AF assist would take 3 times but then once achieved it was quick. So if unsure off AF consistency do the full press for the first shot then half press for subsequent shots. I'm going to try it out.

This may be an excellent "temporary" solution but I'm still won't be thrilled about changing my shooting style.

Thanks Michael for running that time comparison! A lot of folks had that exact question in their minds for a couple of months now!

I imagine 70 seconds would seem like an hour if you were shooting a wedding with everyone staring at you as the seconds tick by, and you start to sweat.

5d3 owner here, has used it on multiple weddings. I don't find the lag time to be too much of an issue because the AF lag only happens in extremely dark situations -- like when your going with no flash ISO 6400-12,800, f2.8 or lower, 1/50th SS ---- in the kind of situations you probably would get a shot at all with a 5d2 or 7d. For a while i was running with the 7d 5d3 combo and found that yes, the 7d would achieve focus quicker, but the shot was totally unusable...

shot posted from a reception, ISO 6400, f2.8, 1/100th, 140mm

Also, i have found the focus speed to vary depending on lens used, and aperture used, and which AF mode I'm in. Using either of my primes wide open, with single point AF the lag is much more noticable. But, at f2.8-4 losck is achieved much quicker. And if I used expanded AF points focus is also quicker (less precise though). I see it as a trade off, if I am shooting wide open on prime lenses, I'll accept the lag time in order to get a precise shot! So for me, while it would be nice if it locked quicker, I'll take the trade off!

I don't have a 1D series camera currently, but in the past I always had the feeling that the 1D series had a bit of extra lag when using flash compared to any of the xxD series. I believe this wasn't the case with the original 1D, but started with the 1DII or 1DIIN. It may be that the 5D3 has inherited this from the 1D series, along with the AF system generally, perhaps trading speed for accuracy.

Sadly my 1DX suffers from the same lag as the 5D3. I've been using both quite a lot in the past few months and the delay to lock focus is painful when you have people posed and waiting for the shot to happen.

Michael -- re 70 seconds. what EV level are we talking about? I can see the evidence of more accurate AF here, in the 5D3, perhaps via more retries and/or higher credence level before the system is satisfied. But I want to know do these numbers represent a severe corner case test or a comon real-world scenario? even the speed deamon 5Dii took 45 seconds which is also an eternity if you have groomsmen in black tuxdos in a dimly lit church foyer.

I'm getting the feeling, from the wide variety of responses on this topic, that:

1. we still do not have a solid, consistent, "repeatable by a monkey" use case representing a real scenario consistent with the marketing language, that would communicate to Canon that the camera does not function in the way it was advertized.

2. there may even be some hardware related component here that is similarly not well understood. Canon may have even changed something in the manufacturing process that would reduce the exposure of this problem to older 5D3s . I wonder, for example, what portion of the mis-behaving 5D3s have s/n lower than RustyTheGeek's replacement camera?

...i have found the focus speed to vary depending on ... aperture used, and which AF mode I'm in. Using either of my primes wide open, with single point AF the lag is much more noticable. But, at f2.8-4 losck is achieved much quicker.

If true, that's certainly a firmware design choice by Canon. AF is always done wide open, regardless of the selected aperture. It's possible that Canon elected to trade speed for accuracy when a narrower aperture is selected and the tolerance for slight AF errors is higher.